This application incorporates by reference Taiwanese application Ser. No. 089103293, Filed Feb. 24, 2000.
1. Field of Invention
The present invention relates to a method and apparatus for estimating a radial speed of an optical disk. More particularly, the present invention relates to a method and apparatus applied in an optical storage device for estimating a radial speed without being affected by eccentric phenomenon.
2. Description of Related Art
As demand for high capacity storage medium increases, optical discs become more important. Research into methods of rapidly and reliably reading data stored in the optical disc has become a major effort for all manufacturers.
FIG. 1 is a structure diagram for illustrating conventional servo controllers of an optical storage device. A disc 102 is put upon a spindle motor 104 and rotated by the spindle motor 104. Digital data stored in a plurality of tracks on the disc 102 is read by an optical pick-up 106. The optical pick-up 106 is assembled on a sled 108 and moved to a suitable position by moving the sled 108 via a sled motor 110 for reading data stored in the disc 102.
FIG. 2 is a function block diagram of the servo controller of the optical storage device shown in FIG. 1. Referring to FIGS. 1 and 2, the spindle motor 104 begins to rotate when the optical storage device is activated. Laser diode within the optical pick-up 106 emits a laser and a focusing mechanism is activated by the servo controller of the optical storage device. The focusing mechanism focuses the laser beam reflected off the optical disc 102 onto an optical sensor 204 of the optical pick-up 106. Then, the servo controller activates a tracking mechanism such that the optical pick-up 106 locks the tracks to be read. The optical sensor 204 of the optical pick-up 106 is used for receiving optical signals of the laser beams reflected by the disc 102 and then transforms these optical signals into electric signals that are further processed by a pre-amplifier 206. The pre-amplifier 206 then outputs analog signals to a control chip 208. The analog signals can be radio frequency (RF) signals related to the data, focusing error (FE) signals, tracking error (TE) signals, radio frequency ripple (RFRP) signals etc., of which the focusing error signals are used to control the focusing operation of the optical pick-up 106.
The control chip 208 outputs control signals to power amplifiers 210 and 212. Output signals of the power amplifier 210 are then transmitted to a lens actuator 214 for controlling fine adjustments of the focusing, tracking and seeking operations of the lens, while output signals of the power amplifier 212 are transmitted to a sled motor 216 for controlling rough adjustments of the tracking and seeking operations of the optical pick-up. The resulting data of the lens actuator 214 and the sled motor 216 are fed back to the optical sensor 204 and, in this way, the optical pick-up 106 can successfully read data stored in the disc.
The lens mounted on the optical pick-up 106 moves up and down vertically until the reflected laser beam focuses on the optical sensor 204. The tracking operation means that the lens mounted on the optical pick-up 106 is fine adjusted in short horizontal distances such that spots, generated by the laser beams and then focused through the lens, can lock the demanded tracks on the disc 102. As for the seeking operation, the lens mounted on the optical pick-up 106 and the sled 108 move horizontally to find the target tracks on the disc 102. In addition, a complete sinusoidal signal is generated in track crossing signal, such as the TE signal or the RFRP signal, while the optical pick-up jumps one track.
Referring to FIG. 3, which shows a timing diagram of a tracking error signal TE, a tracking error zero cross signal TEZC, a radio frequency ripple signal RFRP, and a radio frequency ripple zero cross signal RFZC respectively. The TE signal is used to indicate tracking errors; namely, when the spots focused on the disc have an offset relative to target track, the TE signal also varies according to the offset. At time t0, t2, is and t4, the spots are correctly focused on the target tracks of the disc 102, and therefore the voltage of the tracking error signal TE is Vref and the slopes of the tracking error signal TE corresponding to time t0, t2 and t4 are positive. At time t1 and t3, spots are focused between two adjacent tracks. At these times, the potential of the tracking error signal TE is also Vref, but the slopes of the tracking error signal TE corresponding to time t1 and t3 are negative. When the track is locked, the tracking error signal TE maintains as Vref. The tracking error zero cross signal TEZC can be obtained by comparing the tracking error signal TE with the reference potential Vref. When the tracking error signal TE is larger than Vref, TEZC signal is high; otherwise it is low.
In addition, the radio frequency ripple signal RFRP is defined as the difference between the upper envelope and the lower envelope of the radio frequency signal RF. When the spot is focused on the track of the disc 102, the RFRP signal reaches a peak value; when the spot is focused between tracks of the disc 102, the RFRP signal reaches a bottom value. The phase of the RFRP signal leads the phase of the TE signal by 90 degree when the optical pick-up 106 shifts outwards with respect to the disc 102, and the phase of the RFRP signal lags behind the phase of the TE signal by 90 degree when the optical pick-up 106 shifts inwards with respect to the disc 102. Therefore, by detecting the phase difference between the RFRP signal and the TE signal, the direction of the optical pick-up 106 shifting with respect to the disc 102 is obtained. Furthermore, when the amplitude of the RFRP signal is larger than the average value of the RFRP signal, the RFZC signal is high, otherwise low.
The number of track jumped by the optical pick-up 106 is obtained by calculating the number of the rising edges of the TEZC signal or the RFZC signal. The period T between two adjacent rising edges is defined as taken in jumping one track. The inverse of T is defined as a relative radial speed Vld of the optical pick-up 106 with respect to the disc 102. For example, as shown in FIG. 3, in the period to t0 t4, the optical pick-up 106 crosses two tracks and the radial speed Vld is 2/(t4-t0) Hz.
FIG. 4 shows an eccentric phenomenon for the disc, which generally exists in all discs. The eccentric phenomenon results from manufacturing errors during the manufacturing of the discs, or clamping errors while the disc is put on the spindle motor 104. The tracks on the disc have a common center, which is called an ideal disc center O1; while the disc is put on the spindle motor, the disc is rotated against the eccentric disc center O2, or called the center of the spindle motor 104. As shown in FIG. 4, the distance between the centers O1 and O2 is defined as an eccentricity of the disc 102.
Referring both to FIGS. 4 and 1, when the optical storage device system activates the focusing operation but does not activate the tracking servo control, the horizontal position of the optical pick-up 106 is fixed at location P. If no eccentricity exists, the center O2 of the spindle motor 104 is the same as the ideal disc center O1. Consequently, when the spindle motor 106 rotates at frequency FRQ, no radial speed exists and the optical pick-up is locked along the track. In contrast, if the eccentricity exists, the center O2 of the spindle motor 104 is not coincided with the ideal disc center O1. Consequently, a radial speed component periodically exists between the disc 102 and the optical pick-up 106 when the spindle motor 106 rotates at a frequency FRQ. Then, the TE and RFRP signals are asserted as sinusoidal waveform.
In addition, when the optical pick-up is fixed at the location P, when the tracking and seeking servo controls are not activated, the circle 402 is the trajectory of the optical pick-up 106 crossing the disc 102 when the spindle motor 104 rotates one circle. The circle 404 is the outermost trajectory of the optical pick-up 106 crossing the disc 102 while the circle 406 is the innermost trajectory of the optical pick-up 106 crossing the disc 102. The circle 402 is centered at O2 with a radius L2. The Line O1O2 intersects the circle 402 at points P1 and P2 respectively. The circle 406 is centered at O1 with a radius O1P1, while the circle 404 is centered at O1 with a radius O1P2. 
FIG. 5 shows waveforms of the TE and RFRP signals when the disc contains the eccentricity and the optical pick-up is fixed at the location P. From the TE and RFRP signals detected by the optical pick-up 106, during the time interval that the disc is rotated half circle (before time t5), the optical pick-up 106 is clockwise trajected on the disc 102 from P1 to P2 such that the optical pick-up 106 moves outwards relative to the disc 102, the disc 102 moves inwards. Accordingly, the radial speed Vld varies from slow to fast, and then from fast to low until the optical pick-up 106 moves inwards relative to the disc 102 at time t5. Namely, in another half circle in time period t5 to t6, the optical pick-up 106 clockwise moves from P2 to P1 such that the optical pick-up 106 moves inwards relative to the disc 102 due to that the disc 102 moving outwards. Accordingly, the radial speed Vld varies from low to fast, and then from fast to low until the optical pick-up 106 moves outwards relative to the disc 102 at time t6. 
FIGS. 6A and 6B shows waveforms of the control force signals for pushing the sled during long seeking process. The eccentricity of the disc causes the optical storage device system to be unstable, as shown in waveform of the control force signals FMO. During the speed feedback control of the long seeking, the radial speed Vld of the optical pick-up 106 with respect to the disc 102 is compared with a predetermined speed profile of the optical pick-up 106 for obtaining a speed error signal which is the difference of the radial speed Vld and the predetermined speed profile. The speed error signal is then inputted to the control chip 208 to generate the control force signal FMO to the power amplifier 212 for controlling the seeking operation of the sled motor 216 such that the optical pick-up 106 moves according to the predetermined speed profile.
FIG. 6A shows a waveform of the control force without eccentricity, while FIG. 6B shows a waveform of the control force with eccentricity. Comparing FIGS. 6A and 6B, if there is no eccentricity, the waveform of the control force signal FMO of the sled 108 becomes smoother. The radial speed Vld of the optical pick-up 106 with respect to the disc 102, calculated from the track crossing signal, will contain a radial speed Vd of the disc 102 with respect to the ground while the eccentricity exists, resulting in that as shown in FIG. 6B the control force signal FMO is considerably unstable. The sled is unstable accordingly, and the system also becomes unstable. Furthermore, the tracking stability when the seeking operation is finished becomes worse. In a high speed system, the system efficiency is lowered due to the eccentricity.
The traditional method cannot quantize and compensate the eccentricity, and therefore, system trouble shooting due to the eccentricity cannot be solved.
As embodied and broadly described herein, the invention provides an apparatus and method for estimating a radial speed of the disc, and further, a radial speed of an optical pick-uprelative to ground is obtained for controlling the seeking and tracking operations. Therefore, the seeking servo control is not affected by the eccentric phenomenon. The stability of the seeking operation or tracking operation increases, and so does the access rate.
It is one objective of the present invention to provide an apparatus for estimating a radial speed of a storage media. The apparatus is used in an optical storage device for receiving a pulse signal and an eccentricity, and generating an estimated radial speed of the storage media. The apparatus comprises a frequency detector and a sinusoidal wave generator. The frequency detector is used for receiving the pulse signal and then outputs a rotation frequency. The sinusoidal wave generator is used for receiving the rotation frequency and the eccentricity, and then outputs an estimated radial speed value of the storage media. As mentioned, the estimated radial speed has an amplitude related to the eccentricity and the rotation frequency, and a frequency related to the rotation frequency, and when a jump direction is changed, the estimated radial speed is zero-crossing.
It is another objective of the present invention to provide a method of estimating a radial speed of a disc. The method is designed for an optical storage device, wherein a pulse signal is outputted from a driving chip of a spindle motor of the optical storage device. First, an eccentricity of the storage media is obtained. Next, a rotation frequency of the spindle motor from the pulse signal is calculated when a track crossing direction of the disc is changed. Then, an estimated radial speed of the storage media, which is a sinusoidal signal, is generated from the eccentricity and the rotation frequency. The estimated radial speed has an amplitude related to the eccentricity and the rotation frequency, and a frequency related to rotation frequency, and when a jump direction is changed, the estimated radial speed is zero-crossing.
It is still another objective of the present invention to provide a control chip, which is used for an optical storage device capable of controlling an optical pick-up for reading data stored in a storage media, wherein the control chip receive a track crossing signal and a pulse signal. The control chip comprises a direction detector, an eccentricity detector, a radial speed estimator and a seeking algorithm unit. The direction detector is used for receiving the track crossing signal and then outputs a track crossing direction signal. The eccentricity detector is used for receiving the track-crossing signal and then generates an eccentricity of the disc. The radial speed estimator is used for receiving the eccentricity, the pulse signal and the track crossing direction signal, and then outputs an estimated radial speed of the disc. The seeking algorithm unit is used for receiving the track crossing signal to generate a relative radial speed of the optical pick-up with respect to the disc, for receiving the estimated radial speed of the disc to output an estimated speed of the optical pick-up with respect to the ground. As mentioned, the estimated radial speed has an amplitude related to the eccentricity and the rotation frequency, and a frequency related to is equal to the rotation frequency, and when a jump direction is changed, the estimated radial speed is zero-crossing.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.